higgs boson search with l3 at lep ii
DESCRIPTION
Higgs Boson Search with L3 at LEP II. Steve Muanza, IPN Lyon (France). Outline Theoretical Aspects LEP II Collider and L3 Detector Search for SM Higgs Boson in L3: Production Mechanisms and Cross Section Decay Modes and Final State Topologies SM Backgrounds Four jet channel - PowerPoint PPT PresentationTRANSCRIPT
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Steve Muanza BNL Seminar, 2 May 2002 1
Higgs Boson Searchwith L3 at LEP II
Outline • Theoretical Aspects• LEP II Collider and L3 Detector• Search for SM Higgs Boson in L3:
• Production Mechanisms and Cross Section• Decay Modes and Final State Topologies• SM Backgrounds• Four jet channel• “Missing Energy” channel• Leptonic channels• L3 Channels Combination• L3 Limit• Combination with other LEP Experiments
• Conclusions and Perspectives
Steve Muanza, IPN Lyon (France)
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Steve Muanza BNL Seminar, 2 May 2002 2
Theoretical Aspects
0
Higgs Mechanism in SM
00 2 and Mass Generation• Gauge Bosons:
• • •
• Charged Fermions:•
• Higgs Boson:• v2Hm
2vf
fm
02cos
v2
v
W
m
gm
gm
Z
W
GeV246v 2-
Hparticleneutralscalar1
22 ||||)( V
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Steve Muanza BNL Seminar, 2 May 2002 3
Theoretical AspectsTheoretical Indirect Constraints
on Higgs Boson Mass
Triviality: of the coupling
Vacuum stability: 0)(
2||
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Steve Muanza BNL Seminar, 2 May 2002 4
Theoretical AspectsExperimental Indirect Constraints on Higgs Boson Mass
)%957.22
(
)%680.12
(5434
19685
CLH
CLH
GeVmGeVm
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Steve Muanza BNL Seminar, 2 May 2002 5
LEP II Collider
Located at CERN (R=4.2 km)4 Experiments: ALEPH, DELPHI, L3, OPAL
• LIL: 600 MeV • EPA• PS: 3.5 GeV• SPS: 22 GeV• LEP
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Steve Muanza BNL Seminar, 2 May 2002 6
LEP II ColliderCollided e+e-
LEP I (1989-1995)LEP II (1996-2000)
stX 22
)(
1
189
465.2
ADLOGeVs
fbLdt
130136
6.15.8
161172
10.810.2
183 55.5
189 176.4
192196200202
29.884.183.337.1
202-206206-209
145.372.0
)(GeVs
L3 Integrated Luminosity )( 1 pbLdt
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Steve Muanza BNL Seminar, 2 May 2002 7
L3 Detector
TEVATRON
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Steve Muanza BNL Seminar, 2 May 2002 8
L3 DetectorParticle/Object ID
05.0%55
0008.0%4.0%8.2:
EE
EEE
rCalorimete
Jet
EM
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Steve Muanza BNL Seminar, 2 May 2002 9
Analyses: Higgs Boson Production
Signal Cross SectionProduction Mechanisms
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Steve Muanza BNL Seminar, 2 May 2002 10
B-tagging is crucial
Analyses: Higgs Boson Decays
Higgs Boson Branching Fractions
%1.10)(
%0.20)(
%9.69)(
ZBR
ZBR
qqZBR
Z Boson Branching Fractions
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Steve Muanza BNL Seminar, 2 May 2002 11
Analyses: Higgs Boson DecaysSignal Topologies (82%)
)115( GeVmH
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Steve Muanza BNL Seminar, 2 May 2002 12
Analyses: Higgs Boson DecaysNexp(mH=115 GeV)
Channel DATA B S
12 9.4 1.8 5 3.3 0.66 0 0.38 0.14 0 0.26 0.11 1 0.14 0.03 0 0.84 0.15
Total 18 14.3 2.9
GeVs 209200
05.0BS
H
H
eHe
HqHq
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Steve Muanza BNL Seminar, 2 May 2002 13
Analyses: SM Backgrounds
Main Backgrounds
)(qqee
ZZee
WWee
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Steve Muanza BNL Seminar, 2 May 2002 14
Analyses: Search Strategy
Loose Preselection(Topology)
Tight Preselection
Multivariate Selection(NN or Likelihood)
Mass Discriminant
Final Discriminant
Signal EstimatorConfidence Levels
Main variable:B-tagging
Constrained KinematicFits (5C or 4C)
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Steve Muanza BNL Seminar, 2 May 2002 15
Analyses: B-Tagging
L3 Implementation
NN combination of:•Non-isolated muon tagging,•Non-isolated electron tagging,•Decay length (high IP tracks),•Explicit 2ndary vertex reco.,…
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Steve Muanza BNL Seminar, 2 May 2002 16
Analyses: Higgs Boson Mass Reconstruction
HZee
ff
)(
Z
bbH
ffZ mm
mmm
orbbH
Use kinematic fits• Aim: Improve the mass resolution • Method: do the HZ kinematic hypothesis • Take advantage of:
• Momentum conservation (3C)• Energy conservation (1C)• Mass constraint (1C)
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Steve Muanza BNL Seminar, 2 May 2002 17
Analyses: 4j Channel)(/* qqZ 'qqWW
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Steve Muanza BNL Seminar, 2 May 2002 18
Analyses: 4j Channel
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Steve Muanza BNL Seminar, 2 May 2002 19
Analyses: 4j Channel
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Steve Muanza BNL Seminar, 2 May 2002 20
Analyses: 2j+Emiss Channel
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Steve Muanza BNL Seminar, 2 May 2002 21
Analyses: 2j+Emiss Channel
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Steve Muanza BNL Seminar, 2 May 2002 22
Analyses: 2j+Emiss Channel
0.95)btag(jet0.61)btag(jet
0.115m
6.106m4.99m
2
1
recH
vis
mis
GeV
GeVGeV
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Steve Muanza BNL Seminar, 2 May 2002 23
Analyses: 2j+Emiss Channel
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Steve Muanza BNL Seminar, 2 May 2002 24
Analyses: 2j+Emiss Channel
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Steve Muanza BNL Seminar, 2 May 2002 25
L3 Detector
99.3
4238
)1996(
EGAP
FibersingScintillatLead
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Steve Muanza BNL Seminar, 2 May 2002 26
Checking the EGAP response
Analyses: 2j+Emiss Channel
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Steve Muanza BNL Seminar, 2 May 2002 27
Checking the EGAP responseAnalyses: 2j+Emiss Channel
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Steve Muanza BNL Seminar, 2 May 2002 28
Analyses: ¨Lepton¨ Channel
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Steve Muanza BNL Seminar, 2 May 2002 29
Analyses: ¨Lepton¨ Channel
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Steve Muanza BNL Seminar, 2 May 2002 30
Analyses: Limits Derivation Statistical Estimator
):(
)()(
22
iesprobabilitPoissonofproduct
BdataBSdata
LnQLn
)1(1 i
iN
iitot b
sLnnsQLnbins
needsonecandaditesobservedmoretheisithighestthesectioncrossd)(integratesignalthetorelateddirectly:
tots
candidatetheislike"signal"moretheisithighestthe
ratio(local)thetorelated:)1( BS
ibis
i Lnw
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Steve Muanza BNL Seminar, 2 May 2002 31
Analyses: L3 Search Results
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Steve Muanza BNL Seminar, 2 May 2002 32
Analyses: L3 Search Results
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Steve Muanza BNL Seminar, 2 May 2002 33
Analyses: Limits Derivation Confidence Levels
CLs (1-CLB) : measures resp. the incompatibility between the observed events and the S (B) hypothesis (resp. exclusion / discovery CL)
Exclusion: CLS= CLS+B / CLB
CLS < 5% (S hypothesis excluded at 95% CL)Discovery: 1-CLB < 2.7x10-3 (3signal ¨hint¨) 1-CLB < 5.7x10-7 (5actual signal discovery)
Systematics uncertainties are accounted for by varying (gaussian distr.) S and B in the MC trials
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Steve Muanza BNL Seminar, 2 May 2002 34
Analyses: L3 Search Results
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Steve Muanza BNL Seminar, 2 May 2002 35
Analyses: L3 Search ResultsSystematic Uncertainties
• Overall systematics:• Signal: 4%• Background: 8-10%
• + qq background (populates the high mass region for 4j and 2j+Emiss channels)• Uncertainty on Nexp(background): 6-15% • Uncertainty on Nexp(signal): 3-6% (Both for mH close or beyond HZ kinematic limit)
LEPECM=30 MeVLumi: 1%
Theory
AnalysesTopological cuts: tagging: 3-5% MC Stat.: 2% (S)
8% (B)
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Steve Muanza BNL Seminar, 2 May 2002 36
Analyses: LEP Search Results
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Steve Muanza BNL Seminar, 2 May 2002 37
Analyses: LEP Search Results
Rank Expt ECM Channel Weight@115 GeV
1 ALEPH 206.7 4j 114.3 1.73
2 ALEPH 206.7 4j 112.9 1.21
3 ALEPH 206.5 4j 110.0 0.64
4 L3 206.4 2j+Emiss 115.0 0.53
5 OPAL 206.6 4j 110.7 0.53
6 DELPHI 206.7 4j 114.3 0.49
)(GeVmrecH
Most Significant Candidates
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Steve Muanza BNL Seminar, 2 May 2002 38
Analyses: LEP Search Results
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Steve Muanza BNL Seminar, 2 May 2002 39
Analyses: LEP Search Results
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Steve Muanza BNL Seminar, 2 May 2002 40
Analyses: LEP Search Results
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Steve Muanza BNL Seminar, 2 May 2002 41
Analyses: LEP Search Results
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Steve Muanza BNL Seminar, 2 May 2002 42
Analyses: LEP Search Results
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Steve Muanza BNL Seminar, 2 May 2002 43
Analyses: LEP Search Results5.0
BS
0.1BS
GeV109m recH
0.2BS
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Steve Muanza BNL Seminar, 2 May 2002 44
Conclusions
• L3: No signal observed (despite the interesting candidate)• Limit:
• LEP: Interesting excess observed 2.1• Compatible with a background fluctuation • ¨Compatible¨ with a 115 GeV signal • The case is still open!!!• Limit:
GeV112.4m
GeV112.0mexpH
obsH
GeV115.4m
GeV114.1mexpH
obsH
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Steve Muanza BNL Seminar, 2 May 2002 45
Prospects at TEVATRON Run II